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Do Floods Hurt or Help Fish?

Flooding along the Mississippi River continues to dominate headlines, as Mississippi and Louisiana brace for record water levels. The river has already reached a record 58 feet in Natchez, Mississippi, and is expected to crest there at 64 feet on May 21, while Louisiana officials nervously consider whether to open the Morganza spillway, which would lower the river by several feet, but also deluge thousands of homes and businesses. Cities farther upstream, though, aren't letting days of flooding get in the way of events: Memphis is even going ahead with a World Championship BBQ competition. Of course, humans aren't the only creatures affected by the flood; what about wildlife along the river? For instance, does flooding help or hurt fish populations?

Well, while the answer varies from flood to flood, indications are that, on the Mississippi, a large flood will help fish populations. A little over a decade ago, John Hickey of the Army Corps of Engineers and Jose Salas of Colorado State compiled a number of smaller studies of various floods' effects on local flora and fauna.  (Rivers studied included the Mississippi, the Missouri, the Colorado, and the Illinois, among others.) In some cases, floods lead to a decline in fish population. In these situations, fewer young fish survive than normal, as the offspring are isolated by the retreating waters after the flood. But such declines are more common in faster-moving rivers; on rivers that are slower-moving, and surrounded by floodplains, like the Mississippi, flooding typically increases both the number of plankton and the size of the spawning area. Both of these increases raise survival rates, and, furthermore, the duration of this year's flood makes it unlikely that juveniles will be stranded by retreating water levels. Indeed, fishers along the Mississippi say that 1993 was one of the best years ever for fish numbers. All we can do for now, though, is wait, and see. In the meantime, to donate to relief efforts, visit the Red Cross's website.